1. Field of the Invention
The present invention relates generally to cooling systems for steam generators used in power plants and the like, and particularly to an air cooling system and method for a heat recovery steam generator inlet that provides temperature reduction control for a heat recovery steam generator (HRSG) air inlet to mitigate overspray during an inter-stage cooling procedure performed in a desuperheater.
2. Description of the Related Art
Combined cycle and cogeneration are processes that use the exhaust heat discharged from a Combustion Turbine (CT) to provide heat to a boiler, which, in turn, makes steam to power a Steam Turbine (ST). A heat recovery steam generator (HRSG) is a boiler that has an inlet coupled to an exhaust of a CT engine or other heat source and typically includes an inter-stage desuperheater.
Desuperheater overspray is a term used to describe a condition where spray water from an inter-stage desuperheater in an HRSG is not fully evaporated prior to entering the downstream superheater or reheater and associated piping.
Water quenching from desuperheater overspray has caused a number of superheater and reheater tube failures in HRSGs. Piping damage has also occurred at some plants, due to un-evaporated spray water quenching the pipe wall.
This problem is particularly prevalent in HRSGs behind large CTs where exhaust gas temperature reaches a peak of 1200° F. when operating at low load or during startup. This operating condition is challenging from a superheater or desuperheater design perspective, as it results in a combination of low steam flow and high spray water flow, which yields a high likelihood of desuperheater overspray. While many systems use water injection to cool the turbine exhaust, such cooling results in thermal fatigue damage (quench) to non-pressure parts in the inlet duct, wastes expensive treated boiler water that cannot be recovered, and is insufficient to accomplish cooling of the turbine exhaust gas without additional overspray in the desuperheaters.
Thus, an air cooling system and method for a heat recovery steam generator (HRSG) inlet solving the aforementioned problems is desired.